Horizontal stabilizers for current transport aircraft are adjustable in their setting to the axis of the aircraft. An additional torque about the pitch axis of the aircraft can be generated by this change of the blade angle of the horizontal stabilizer in order to establish trimming conditions or to support the effect of the elevators during maneuvers.
In aircraft construction, systems critical for safety, which also include the horizontal stabilizer adjustment system THSA (=trimmable horizontal stabilizer actuator), have to be secured against simple mechanical failures. For this reason, all load-bearing components of a THSA are designed such that at least two independent mechanical load paths arise from the force introduction points from the horizontal stabilizer up to the connection to the aircraft structure (fail-safe principle).
The fail-safe architecture of a conventional stabilizer system such as is used in transport aircraft today is represented by way of example with reference to FIG. 1. The mechanical power in this system is guided by two drives or motors 1a and 1b via a speed summing differential transmission 2 to a spindle 3 whose spindle nut 4 moves in a translatory manner and thus imposes a pivot movement on the rotatably supported horizontal stabilizer 5.
The motors 1a and 1b are fed by two mutually independent energy systems 6a and 6b and are controlled by a control and monitoring electronic system (motor control electronics MCE) 7a and 7b. Each drive 1a and 1b is provided with a brake (power off brake, POB) 8a and 8b whose braking effect is generated by a biased spring. The spring is relaxed at the command of the respective MCE unit 7a and 7b via an actuating mechanism which draws its power from the energy system of the associated drive 1a and 1b. If the energy system 6a and 6b or the electronics 7a and 7b are not available anymore due to a failure, the POB 8a and 8b is set automatically. This procedure is also called the power-off principle. The differential transmission 2 has the required two independent load paths and is designed such that half a sum of the speeds of both motors 1a and 1b is always transmitted to the output shaft 9. If a motor 1a or 1b is stopped due to an occurring failure and if the corresponding transmission input is blocked with the associated POB 8a or 8b, the remaining intact drive 1a or 1b continues to drive the output shaft 9 at a reduced speed. The power is transmitted to the spindle 3 via a further transmission 10.
Two independent load paths are integrated in the spindle structure, of which one primary load path formed by the actual function spindle 3 bears the complete load in the failure-free operating case, whereas a secondary load path has no load in the failure-free operating case. This secondary load path 11 is realized as a tension rod 11 in the interior of the hollow spindle 3. If the spindle 3 breaks, it is held together by the tension rod 11 so that the force transmission is maintained over the held-together spindle 3 and the spindle nut 4 likewise made in duplicate mechanically and the horizontal stabilizer 5 is fixed with respect to the structure. Both the spindle head 12 of the primary load path and the secondary load path 11 inside the spindle 3 are gimbal-mounted at the aircraft structure. The secondary load path 11 is, for example, gimbal-mounted via a ball and socket joint 13. A so-called “no-back” 14 protects the adjustment system and so the stabilizer against an uncontrolled escape from a secure holding position under the effect of aerodynamic forces at the stabilizer in the case of a simple mechanical failure (e.g. breakage of a drive shaft between the drives 1a and 1b and the differential transmission differential gear 2). The no-back 14 in this case acts as an autonomous mechanical emergency brake.
Apparatus of this type for the adjustment of the horizontal stabilizers for aircraft in accordance with the present prior art are made in duplicate mechanically in all mechanical load-bearing groups—from the transmission 2 and 10 to the spindle head 12, the spindle 3 with secondary load path 11 and motor 4—for reasons of safety. This makes a very complex fail-safe construction necessary which is not testable, or is only testable with limitations, for freedom of failure of both load paths (avoidance of so-called “sleeping failures”). Neither the no-back POB 14 nor the integrated, secondary load path 11 permit an automated test routine in the installed state. With the no-back 14, it is not possible to apply the external loads required for the testing of the function. In modern adjustment systems, a sensor system will be implemented which, following a failure of the primary load path, however, only indicates a load on the tension rod in operation. The previously described complex construction and the automatable testability of the system on the ground, which is only possible in a very restricted manner or even not completely at all, are the major serious disadvantages of the apparatus for the adjustment of the horizontal stabilizers for aircraft of the prior art.
It is one object of the present disclosure to further develop a generic apparatus for the adjustment of horizontal stabilizers for aircraft in relation to the axis of the aircraft with a mechanical power transmission between the aircraft horizontal stabilizer and the aircraft structure such that fail-safe system is mechanically ensured and that it is permitted to test all load-bearing elements of the structure in an automated manner on the ground. In one embodiment it is desired to be able to perform automated testing without any special tools, load simulation or similar.
This and other objects may be solved in accordance with an apparatus for the adjustment of horizontal stabilizers for aircraft in relation to the aircraft axis with a mechanical power transmission of two drives to the horizontal stabilizer is provided in which two differential transmissions coupled via a connection shaft drive the horizontal stabilizer via a mechanical transmission, such as one spindle and one spindle nut each. Accordingly, instead of a secondary load path integrated in the spindle—such as has been customary up to the present day in accordance with the aforesaid discussion of the prior art—a structure is formed with two mechanically separate primary load paths. These two separate primary load paths may respectively include: differential transmissions, transmission output shafts, transmissions, spindles and spindle nuts up to the plate on the horizontal stabilizer, each made simply in a mechanical construction manner.
In one example, the two differential transmissions can also effect an automatic load and speed synchronization of the spindles with different speeds of the drives.
Also, the apparatus each only have simply load-bearing components.
A speed sensor for the determination of the speed of the connection shaft and a shaft brake for the braking of the connection shaft may be particularly advantageously present, which allow cases of breakage in a mechanical component of the power-carrying load paths to be recognized and to reliably fix the system in the case of failure.
It is furthermore advantageous for shaft brakes and sensors to be arranged in each case on the drive shafts arranged between the drives and the differential transmissions and for additional sensors to be present for the speed recognition of the transmission output shafts. Mechanical failures and the function capability of all brakes can be determined using automatable test routines via MCEs likewise advantageously present for the evaluation of the sensor signals. An integrity test of the total system is thus possible on the ground.
The drives and brakes can advantageously be based on hydraulic power supply, electric power supply or a combination thereof.